1. Field of the Invention
The present invention relates to a display device using a printed circuit board (PCB) as a substrate of a display panel. More particularly, the present invention relates to a display device capable of improving the response speed and image quality thereof by directly connecting pixels or segments of a display panel to a driving circuit through a via hole formed in a PCB.
2. Description of the Prior Art
Generally, display devices are classified into emissive display, such as CRTs, PDPs, LEDs, or OLEDs, and non-emissive display, such as LCDs. The emissive display represents the high response speed, but the image becomes faint in a bright place. In contrast, the non-emissive display represents the low response speed although it can clearly display the image in the bright place.
Among other things, an electrochromic display (ECD) is a non-emissive display, such as an LCD, capable of adjusting the color of an electrochromic material through controlling the chemical reaction of the electrochromic material by applying an electric signal to the electrochromic material.
FIG. 1 is a schematic view illustrating a structure of a display panel of an ECD. Referring to FIG. 1, the display panel 1 of the ECD includes a lower electrode 11 formed on a lower glass substrate 10, an electrochromic layer 12 formed on an upper surface of the lower electrode 11 and including an electrochromic material changing its color depending on an electric signal applied thereto, an electrolyte layer 13 formed on the electrochromic layer 12 and including ions related to the electrochromic reaction, an ion storage 14 formed on the electrolyte layer 13 for storing ions having polarity opposite to that of the ions related to the electrochromic reaction, an upper electrode 15 formed on the ion storage 14, and an upper glass substrate 16 formed on the upper electrode 15. Generally, at least one of the lower electrode 11 and the upper electrode 15 is a transparent electrode, such as indium tin oxide (ITO) electrode. The ion storage 14 can be omitted and the electrolyte layer 13 can be replaced with an ionic liquid layer including ionic liquid.
If voltage is applied to the display panel 1, current flows from the electrochromic layer 12 to the ion storage 14, thereby coloring the electrochromic layer 12. In contrast, if the current flows from the ion storage 14 to the electrochromic layer 12, the electrochromic layer 12 is decolored. The above coloring and decoloring reactions of the electrochromic layer 12 may occur with the current flow inverse to the above current flow depending on materials of the electrochromic layer 12.
FIG. 2a is a view illustrating a layout of the electrochromic layer for displaying numerical characters with 7-segments, and FIG. 2b is a view illustrating a layout of a conventional lower electrode for applying an electric signal to the electrochromic layer shown in FIG. 2a. 
As shown in FIG. 2b, lengths of electrodes corresponding to segments are different from each other. In general, an electrode resistance value (for example, 200 Ω) of a segment (a) is higher than an electrode resistance value (for example, 100 Ω) of a segment (d) by two times. In this case, the maximum current for the segments (d and a) is 10 mA and 5 mA, respectively, under the same coloring voltage of 1.0V, so the response speed of the segment (a) is slower than the that of the segment (d) by two times. Accordingly, the overall response speed of the display device may be slowered while varying the coloring degree for each segment, thereby degrading the image quality of the display device.
The above problem may occur in various display devices in addition to the ECD. For instance, display devices, such as the LCDs, OLEDs or PDPs, have wirings on each pixel electrode for applying an electric signal to a display panel. In this case, the line width becomes narrowed as the number of pixels increases, thereby increasing the resistance. Accordingly, the response speed of the display device is slowered and the non-uniformity of the pixel image is occurred.